1. Field of the Invention
The invention relates generally to the field of marine geophysical survey apparatus and methods. More specifically, the invention relates to structures for marine sensor streamers that can be deployed by spooling from a vessel-borne winch or reel.
2. Background Art
In a marine geophysical survey, a survey vessel travels on the surface of a body of water such as a lake or the ocean. The survey vessel typically contains geophysical acquisition control equipment, which includes devices such as navigation control, seismic and/or electromagnetic energy source control, and sensor signal recording devices. The source acquisition control equipment causes an energy source towed in the body of water, by the survey vessel or another vessel, to actuate at selected times. The source may be any type well known in the art of seismic acquisition, including seismic air guns or water guns, arrays of air guns, electrodes, wire coils, magnetometers, etc. Sensor streamers, also called sensor cables, are elongate cable-like structures that are towed in the body of water by the survey vessel or by another vessel. Typically, a plurality of sensor streamers is towed behind the survey vessel laterally spaced apart from each other. The streamers contain sensors to detect the energy wavefields initiated by the energy source and reflected from formation boundaries in the subsurface Earth formations below the water bottom.
The geophysical sensors are typically located at regular intervals along the length of streamers. The streamers may also include electronic components, electrical wiring and may include other types of sensors. The streamers are typically assembled from sections, each section being approximately 75 meters in length. A number of such sections are joined end to end, and can extend the assembled streamer to a total length of many thousands of meters. Position control devices, such as depth controllers, paravanes, and tail buoys may be affixed to the streamer at selected positions and are used to regulate and monitor the movement of the streamer in the water. During operation, the streamers are typically submerged at a selected depth in the water of five to several hundred meters.
Deploying the streamers from the survey vessel is typically performed by unspooling the streamers from one or more winches disposed on the survey vessel. It is desirable that the streamers are relatively flexible during spooling and unspooling to facilitate such action. During operation in the water, however, it is desirable for the streamers to be relatively resistant to flexure, compression and extension so as to reduce the amount of noise induced in the sensors.